Data storage device dynamically generating extended redundancy over interleaves of a data track

ABSTRACT

A data storage device is disclosed wherein a first codeword is generated comprising first redundancy, and a second codeword is generated comprising second redundancy. At least part of the first codeword is written to a first data sector and a second data sector of a first data track on a disk, and at least part of the second codeword is written to a third data sector and a fourth data sector of the first data track different from the first data sector and the second data sector. When an anomaly is detected in the first data sector, first extended redundancy is generated over at least the first data sector and the second data sector of the first data track without generating second extended redundancy over the third data sector and the fourth data sector. Data is recovered from the first data sector based on the first extended redundancy.

BACKGROUND

Data storage devices such as disk drives comprise a disk and a headconnected to a distal end of an actuator arm which is rotated about apivot by a voice coil motor (VCM) to position the head radially over thedisk. The disk comprises a plurality of radially spaced, concentrictracks for recording user data sectors and servo sectors. The servosectors comprise head positioning information (e.g., a track address)which is read by the head and processed by a servo control system tocontrol the actuator arm as it seeks from track to track.

FIG. 1 shows a prior art disk format 2 as comprising a number of servotracks 4 defined by servo sectors 6 ₀-6 _(N) recorded around thecircumference of each servo track. Each servo sector 6 _(i) comprises apreamble 8 for storing a periodic pattern, which allows proper gainadjustment and timing synchronization of the read signal, and a syncmark 10 for storing a special pattern used to symbol synchronize to aservo data field 12. The servo data field 12 stores coarse headpositioning information, such as a servo track address, used to positionthe head over a target data track during a seek operation. Each servosector 6 _(i) further comprises groups of servo bursts 14 (e.g., N and Qservo bursts), which are recorded with a predetermined phase relative toone another and relative to the servo track centerlines. The phase basedservo bursts 14 provide fine head position information used forcenterline tracking while accessing a data track during write/readoperations. A position error signal (PES) is generated by reading theservo bursts 14, wherein the PES represents a measured position of thehead relative to a centerline of a target servo track. A servocontroller processes the PES to generate a control signal applied to ahead actuator (e.g., a voice coil motor) in order to actuate the headradially over the disk in a direction that reduces the PES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servotracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a head actuated over a disk.

FIG. 2B shows an embodiment wherein the data sectors of a data trackform two interleaved codewords, including a first interleave codewordand a second interleave codeword.

FIG. 2C is a flow diagram according to an embodiment wherein when ananomaly is detected in a first data sector of the first interleave,first extended redundancy is generated over at least the first datasector and a second data sector of the first data track withoutgenerating second extended redundancy over a third data sector and afourth data sector of the second interleave.

FIG. 3A shows an embodiment wherein the redundancy of each interleavedcodeword as well as the extended redundancy comprise at least one paritysector which together are capable of recovering two data sectors perinterleave that are unrecoverable at the sector level.

FIG. 3B shows an embodiment wherein the first extended parity sector isgenerated over data sectors of the first interleave when an anomaly isdetected in at least one data sector of the first interleave withoutgenerating the second extended redundancy over data sectors of thesecond interleave.

FIG. 3C shows an embodiment wherein the first extended parity sector isgenerated over a different subset of data sectors in the firstinterleave depending on where an anomaly is detected within the firstinterleave.

FIG. 3D shows an embodiment wherein the first extended redundancycomprises two parity sectors generated over different subsets of thedata sectors in the first interleave to enable recovering three datasectors within the first interleave.

FIG. 3E shows an embodiment wherein the first and second extended paritysectors are generated over different subsets of data sectors in thefirst interleave depending on where an anomaly is detected within thefirst interleave.

FIG. 4 is a flow diagram according to an embodiment wherein the extendedredundancy may be generated for one or both interleaves depending onwhether an anomaly is detected in one or both interleaves.

FIG. 5A is a flow diagram according to an embodiment wherein an anomalyis detected in a data sector during a write operation, such as byevaluating a PES generated while writing the data sectors.

FIG. 5B shows an embodiment wherein different frequency preambles arewritten in data sectors in adjacent data tracks to facilitate generatingthe PES per data sector.

FIG. 6 is a flow diagram according to an embodiment wherein an anomalyis detected in a data sector during a read operation, such as based on asuitable quality metric generated during the read operation.

DETAILED DESCRIPTION

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a head 16 actuated over a disk 18,wherein the disk 18 comprises a plurality of data tracks 20 and eachdata track comprises a plurality of data sectors 22 ₁-22 _(N) (FIG. 2B).The disk drive further comprises control circuitry 26 configured toexecute the flow diagram of FIG. 2C, wherein a first codeword comprisingfirst redundancy 24 ₁ is generated (block 28), and a second codewordcomprising second redundancy 24 ₂ is generated (block 30). At least partof the first codeword is written to a first data sector and a seconddata sector of a first data track, and at least part of the secondcodeword is written to a third data sector and a fourth data sector ofthe first data track different from the first data sector and the seconddata sector (block 32). An anomaly is detected in at least the firstdata sector of the first data track (block 34), and when the anomaly isdetected in the first data sector (block 36), first extended redundancy38 ₁ is generated over at least the first data sector and the seconddata sector of the first data track without generating second extendedredundancy over the third data sector and the fourth data sector (block40). Data from the first data sector is recovered based on the firstextended redundancy (block 42).

In the embodiment of FIG. 2A, the disk 18 comprises a plurality of servosectors 44 ₁-44 _(N) that define servo tracks, wherein the servo sectors44 ₁-44 _(N) may comprise any suitable head position information, suchas a track address for coarse positioning and servo bursts for finepositioning. The data tracks 20 are defined relative to the servo tracksat the same or different radial density. The control circuitry 26processes a read signal 45 emanating from the head 16 to demodulate theservo sectors 44 ₁-44 _(N) and generate a position error signal (PES)representing an error between the actual position of the first head anda reference position relative to a target track. A servo control systemin the control circuitry 26 filters the PES using a suitablecompensation filter to generate a control signal 46 applied to a voicecoil motor (VCM) 48 which rotates an actuator arm 50 about a pivot inorder to actuate the head 16 radially over the disk 18 in a directionthat reduces the PES. The servo bursts may comprise any suitablepattern, such as an amplitude based servo pattern or a phase based servopattern (FIG. 1).

In one embodiment, each data sector 22 ₁-22 _(N) in the data track ofFIG. 2B may comprise any suitable sector level redundancy used torecover the data sector, such as redundancy for implementing a suitableblock code or a suitable iterative code (e.g., a low-density paritycheck (LDPC) code). In some cases, a data sector may becomeunrecoverable using the sector-level redundancy, for example, due toextensive media defects or due to track squeeze from an adjacent datatrack. When a data sector is unrecoverable at the sector level,track-level redundancy may be employed to recover the data sector. Anexample of track-level redundancy is a parity sector generated over aninterleave of the data sectors, wherein the data sectors and paritysectors form a codeword. In an example embodiment shown in FIG. 3A, theodd and even interleaves of data sectors are encoded to generatecorresponding track level parity sectors 52 ₁ and 52 ₂. When a datasector in one of the interleaves is unrecoverable (e.g., data sector 22₃), the other data sectors of the interleave together with the paritysector can be used to recover the unrecoverable data sector. In thisembodiment, the track level parity sectors 52 ₁ and 52 ₂ are capable ofrecovering a single data sector per interleave. In order to increase thetrack level recovery power, in one embodiment extended redundancy may begenerated over the data sectors of a track to enable the recovery ofmore than a single data sector per interleave. In the example of FIG.3A, the extended redundancy comprises an additional parity sector 54 ₁and 54 ₂ per interleave, where each extended parity sector 54 ₁ and 54 ₂is generated over a subset of the data sectors in an interleave. Eachextended parity sector 54 ₁ and 54 ₂ enables the recovery of anadditional data sector per interleave. In the example of FIG. 3A, theextended parity sector 54 ₁ may be used to recover data sector 22 ₉since it is the only unrecoverable data sector of the correspondingcodeword. After data sector 22 ₉ is recovered, data sector 22 ₃ may berecovered using parity sector 52 ₁ since it becomes the onlyunrecoverable data sector of the corresponding codeword. Similarly,extended parity sector 54 ₂ may be used to recover data sector 22 ₁₈,and then parity sector 52 ₂ may be used to recover data sector 22 ₈.Other embodiments may employ further levels of extended parity sectorsgenerated over reduced resolutions of data sectors per interleave tofurther increase the correction power of each interleave. In oneembodiment, multiple levels of extended parity sectors may be generatedduring an access operation, but fewer than all of the extended paritysectors may be stored depending on the number of anomalous data sectorsdetected during the access operation. In yet other embodiments, morethan two first level parity sectors 52 may be generated eachcorresponding to a different interleave of data sectors which increasesthe recovery power of the parity sectors, but decreases the formatefficiency of the disk.

In one embodiment, the control circuitry is configured to detect ananomaly in a data sector and generate extended redundancy (e.g., aparity sector) for the corresponding interleave when the anomaly isdetected. FIG. 3B shows an example of this embodiment wherein thecontrol circuitry may detect an anomaly in a first data sector 22 ₃ anddetect an anomaly in a second data sector 22 ₁₃, both of which are inthe first interleave (the odd interleave). The anomalies may be detectedduring a write operation or a read operation, but in either case, theextended redundancy (e.g. parity sector 54 ₁) is generated for thecorresponding interleave in order to increase the recovery power of theinterleave. For example if the anomalies are detected during a writeoperation, the extended redundancy may be generated for thecorresponding interleave and later used to recover the affected datasectors in the event the data sectors are unrecoverable. In the exampleof FIG. 3B, no anomalies are detected in the second interleave (eveninterleave) and so the extended redundancy (e.g., parity sector 54 ₂) isnot stored, thereby reducing the amount of extended redundancy storedper data track. Reducing the amount of extended redundancy stored may beparticularly useful in an embodiment where the extended redundancy isstored in a non-volatile semiconductor memory (NVSM) such as a Flashmemory which typically has less storage capacity. In an embodiment wherethe extended redundancy is stored on the disk (e.g., in a reserved datatrack), reducing the amount of extended redundancy per data track mayhelp ensure it can be flushed to the disk as part of a power-failoperation.

FIG. 3C shows an embodiment wherein the extended redundancy (e.g. paritysector 54 ₁) may be generated over a different subset of data sectorsthan shown in FIG. 3B depending on which data sector has a detectedanomaly. In the example of FIG. 3C, data sector 22 ₁₁ has a detectedanomaly, and so the extended redundancy (parity sector 54 ₁) isgenerated over a subset of data sectors that includes data sector 22 ₁₁.In one embodiment during a write/read operation to the data track, themultiple parity sectors may be generated over multiple different subsetsof data sectors within an interleave. For example, a parity sector maybe generated over the subset of data sectors shown in FIG. 3B whileconcurrently generating the parity sector over the subset of datasectors shown in FIG. 3C. At the end of the write/read operation to thedata track, the control circuitry may store one of the extended paritysectors depending on which subset an anomalous data sector belongs.

FIG. 3D shows an embodiment wherein the control circuitry may generateand store for an interleave multiple parity sectors with decreasingresolution when more than two anomalous data sectors are detected (e.g.,data sectors 22 ₇, 22 ₁₃, and 22 ₁₇ in the odd interleave). Paritysector 54 ₁ _(_) ₂ is used to recover data sector 22 ₁₇, parity sector54 ₁ _(_) ₁ is then used to recover data sector 22 ₁₃, and parity sector52 ₁ is then used to recover data sector 22 ₇. Similar to the embodimentof FIG. 3C, in FIG. 3D during a write/read operation the controlcircuitry may generate multiple levels of extended parity sectors, andthen store the minimum number of the extended parity sectors neededbased on the number and location of anomalous data sectors detectedafter the write/read operation finishes.

FIG. 3E shows an embodiment wherein an offset is used when generatingthe extended parity sectors 54 ₁ _(_) ₁ and 54 ₁ _(_) ₂ so as to coverdifferent anomalous data sectors within an interleave. In oneembodiment, during a write/read operation the control circuitry maygenerate multiple levels of extended parity sectors as well as extendedparity sectors with an offset as shown in FIGS. 3D and 3E, and thenstore the minimum number of extended parity sectors needed based on thenumber and location of anomalous data sectors detected after thewrite/read operation finishes.

FIG. 4 is a flow diagram according to an embodiment wherein first andsecond data sectors of a first interleave are encoded into a firstcodeword (block 56), and third and fourth data sectors of a secondinterleave are encoded into a second codeword (block 58). The first andsecond codewords are written to a first track (block 60). If during awrite/read operation (block 62) an anomaly is detected in the first datasector of the first interleave (block 64), first extended redundancy isstored that was generated over at least the first and second datasectors of the first interleave (block 66). During a subsequent readoperation, if the first data sector is unrecoverable at the sectorlevel, the first data sector is recovered using the first extendedredundancy (block 68). If during a write/read operation (block 70) ananomaly is detected in the third data sector of the second interleave(block 72), second extended redundancy is stored that was generated overat least the third and fourth data sectors of the second interleave(block 74). During a subsequent read operation, if the second datasector is unrecoverable at the sector level, the second data sector isrecovered using the second extended redundancy (block 76). Accordinglyin this embodiment, the extended redundancy is generated and stored forthe codewords (interleaves) where an anomaly is detected and thereforebenefit from having extended redundancy, and not generated and storedfor the codewords (interleaves) where an anomaly is not detected andtherefore not benefit from having extended redundancy.

FIG. 5A is a flow diagram according to an embodiment wherein during awrite operation (block 78) a first codeword is generated over a firstinterleave of data sectors (block 80), wherein the first codewordcomprises first redundancy (e.g., a parity sector), and a secondcodeword is generated over a second interleave of data sectors (block82), wherein the second codeword comprises second redundancy (e.g., aparity sector). The first and second codewords are written to a firsttrack while checking for write anomalies. If a write anomaly is detectedin a data sector of the first interleave (block 86), first extendedredundancy (e.g., a parity sector) generated over a subset of the firstinterleave is stored on the disk or in a NVSM (block 88). The firstextended redundancy may be generated at any suitable time (block 90),such as during the write operation at block 84, or after a write anomalyis detected at block 86. In one embodiment described above, during thewrite operation multiple extended redundancy (e.g., multiple paritysectors) may be generated over varying subsets of the interleaved datasectors. When an anomaly is detected in a particular data sector atblock 86, the corresponding extended parity sector(s) are stored atblock 88 so they may be used during a subsequent read operation torecover the data sector if needed. Similar operations are executed forthe second interleave of data sectors at blocks 90, 92 and 94 of FIG.5A.

A write anomaly may be detected at blocks 86 and 90 of FIG. 5A in anysuitable manner, such as by monitoring a suitable shock sensor (e.g., apiezoelectric element) or by evaluating the PES generated when readingthe servo sectors. In another embodiment shown in FIG. 5B, a PES for thehead may be generated for each data sector by evaluating a frequencycomponent of the sector preamble field. In this embodiment, the sectorpreamble for data sectors of adjacent data tracks may be recorded atdifferent frequencies such that the corresponding frequency componentsof the read signal may be evaluated to generate a PES at a data sectorsample rate (as compared to a servo sector sample rate). In oneembodiment, the PES may be evaluated for a current data sector beingwritten to a current data track in order to generate and store extendedredundancy for the data sector when needed (when an anomaly isdetected). In another embodiment, the PES may be evaluated while writinga current data sector to a current data track in order to detect a tracksqueeze anomaly for the data sector previously written in the adjacentdata track while writing the data tracks in a shingled format (shingledmagnetic recording (SMR)). In one embodiment, the sector data for eachdata sector of the previously written data track may be saved so thatthe extended redundancy can be generated when an anomaly such as tracksqueeze is detected while writing a current data track. In anotherembodiment, the extended redundancy may be generated for each interleaveof a previously written data track while writing that data track, andthen the corresponding extended redundancy stored if an anomaly isdetected while writing to a current data track. If an anomaly is notdetected in an interleave of a previously written data track or thecurrent written data track, the corresponding extended redundancy may bediscarded.

FIG. 6 is a flow diagram according to an embodiment wherein anomaly in adata sector may be detected during a read operation (block 96). The readoperation may be executed for any suitable reason, such as in responseto a host read command, or as part of a write-verify operation. Forexample, in one embodiment when an anomalous data sector is detectedduring a write operation, instead of storing extended redundancy as partof the write operation the control circuitry may execute a write-verifyread of the data sector. In one embodiment, an anomaly in a data sectordetected during the read operation may be based on any suitable qualitymetric, such as a signal-to-noise ratio (SNR) of the read signal, syncmark quality, number of symbol errors detected, number of codingiterations needed to recover the data sector, etc. When an anomalousdata sector (marginal data sector) is detected (block 100) while readingthe data sectors of a first interleave (block 98), first extendedredundancy is stored on the disk or in a NVSM (block 102). The firstextended redundancy may be generated at any suitable time (block 104),such as during the read operation at block 98, or after a read anomalyis detected at block 100. In one embodiment described above, during theread operation multiple extended redundancy (e.g., multiple paritysectors) may be generated over varying subsets of the interleaved datasectors. When an anomaly is detected in a particular data sector atblock 100, the corresponding extended parity sector(s) are stored atblock 102 so they may be used during a subsequent read operation torecover the data sector if needed. If an anomaly is not detected in aninterleave of the data track, the corresponding extended redundancy maybe discarded. Similar operations are executed for the second interleaveof data sectors at blocks 106, 108 and 110 of FIG. 6.

The track-level extended redundancy 38 ₁ shown in FIG. 2B may begenerated in any suitable manner. In the embodiment where the extendedredundancy 38 ₁ comprises one or more parity sectors, at least oneparity sector may comprise, for example, a hard parity sector may begenerated by XORing the user bits in each of a number of block encodeddata sectors. An unrecoverable data sector may then be erasure correctedby XORing the parity sector with the recovered data sectors tore-generate the unrecovered data sector.

In another embodiment the track level parity sectors and the extendedredundancy parity sectors may be soft parity sectors generated bybit-wise XORing LDPC encoded data sectors. The bit-wise XOR of LDPC codewords results in another valid LDPC sector but also relating the bitsacross the subset of sectors forming additional parity equations. Thisembodiment allows the sector's LDPC code iterations to be combined withsoft parity redundancy of the subset of sectors to allow a separate setof LDPC parity constraints to be applied which are unique relative tothe bitwise XOR operations performed to obtain the track's soft parityconstraints. This embodiment also allows an additional erasurecorrection using the encoded media pattern in lieu of executingadditional iterations when only one failing sector of the extendedredundancy's subset of sectors of the track remains in error which canthen aid convergence of the track level parity for aggregate of failedconvergent sectors of the full track's soft parity.

In other embodiments, the extended redundancy parity sectors may begenerated as both hard and soft parity sectors to extend the protectionof data sectors of a track or subset of sectors of a track which may bebeneficial to the hardware implementation and code execution.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a disk controller, or certainoperations described above may be performed by a read channel and othersby a disk controller. In one embodiment, the read channel and diskcontroller are implemented as separate integrated circuits, and in analternative embodiment they are fabricated into a single integratedcircuit or system on a chip (SOC). In addition, the control circuitrymay include a suitable preamp circuit implemented as a separateintegrated circuit, integrated into the read channel or disk controllercircuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In another embodiment, the instructions are stored on the diskand read into a volatile semiconductor memory when the disk drive ispowered on. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry.

In various embodiments, a disk drive may include a magnetic disk drive,an optical disk drive, etc. In addition, some embodiments may includeelectronic devices such as computing devices, data server devices, mediacontent storage devices, etc. that comprise the storage media and/orcontrol circuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device comprising: a diskcomprising a plurality of data tracks, where each data track comprises aplurality of data sectors; a head actuated over the disk; and controlcircuitry configured to: generate a first codeword comprising firstredundancy; generate a second codeword comprising second redundancy;write at least part of the first codeword to a first data sector and asecond data sector of a first data track; write at least part of thesecond codeword to a third data sector and a fourth data sector of thefirst data track different from the first data sector and the seconddata sector; detect an anomaly in at least the first data sector of thefirst data track; when the anomaly is detected in the first data sector,generate first extended redundancy over at least the first data sectorand the second data sector of the first data track without generatingsecond extended redundancy over the third data sector and the fourthdata sector; and recover data from the first data sector based on thefirst extended redundancy.
 2. The data storage device as recited inclaim 1, wherein: the first data sector and the second data sector format least part of a first interleave of data sectors in the first datatrack; and the third data sector and the fourth data sector form atleast part of a second interleave of data sectors in the first datatrack.
 3. The data storage device as recited in claim 2, wherein thefirst redundancy comprises at least a first parity sector.
 4. The datastorage device as recited in claim 2, wherein the first extendedredundancy comprises at least a first parity sector.
 5. The data storagedevice as recited in claim 3, wherein: the first interleave of datasectors in the first data track comprises a fifth data sector; and thefirst extended redundancy comprises a second parity sector generatedover at least the fifth data sector and exclusive of the first datasector.
 6. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to detect the anomaly in thefirst data sector based on position information of the head detectedwhile writing at least part of the first codeword to the first datasector.
 7. The data storage device as recited in claim 1, wherein thecontrol circuitry is further configured to detect the anomaly in thefirst data sector based on a quality metric generated while reading thefirst data sector.
 8. The data storage device as recited in claim 1,wherein the control circuitry is further configured to write the firstextended redundancy to the disk.
 9. The data storage device as recitedin claim 1, further comprising a non-volatile semiconductor memory(NVSM), wherein the control circuitry is further configured to store thefirst extended redundancy in the NVSM.
 10. The data storage device asrecited in claim 1, wherein the control circuitry is further configuredto: detect an anomaly in at least the third data sector of the firstdata track; and when the anomaly is detected in the third data sector,generate second extended redundancy over at least the third data sectorand the fourth data sector of the first data track; and recover datafrom the third data sector based on the second extended redundancy. 11.A method of operating a data storage device, the method comprising:generating a first codeword comprising first redundancy; generating asecond codeword comprising second redundancy; writing at least part ofthe first codeword to a first data sector and a second data sector of afirst data track on a disk; writing at least part of the second codewordto a third data sector and a fourth data sector of the first data trackdifferent from the first data sector and the second data sector;detecting an anomaly in at least the first data sector of the first datatrack; when the anomaly is detected in the first data sector, generatingfirst extended redundancy over at least the first data sector and thesecond data sector of the first data track without generating secondextended redundancy over the third data sector and the fourth datasector; and recovering data from the first data sector based on thefirst extended redundancy.
 12. The method as recited in claim 11,wherein: the first data sector and the second data sector form at leastpart of a first interleave of data sectors in the first data track; andthe third data sector and the fourth data sector form at least part of asecond interleave of data sectors in the first data track.
 13. Themethod as recited in claim 12, wherein the first redundancy comprises atleast a first parity sector.
 14. The method as recited in claim 12,wherein the first extended redundancy comprises at least a first paritysector.
 15. The method as recited in claim 13, wherein: the firstinterleave of data sectors in the first data track comprises a fifthdata sector; and the first extended redundancy comprises a second paritysector generated over at least the fifth data sector and exclusive ofthe first data sector.
 16. The method as recited in claim 11, furthercomprising detecting the anomaly in the first data sector based onposition information of a head detected while writing at least part ofthe first codeword to the first data sector.
 17. The method as recitedin claim 11, further comprising detecting the anomaly in the first datasector based on a quality metric generated while reading the first datasector.
 18. The method as recited in claim 11, further comprisingwriting the first extended redundancy to the disk.
 19. The method asrecited in claim 11, further comprising storing the first extendedredundancy in a non-volatile semiconductor memory.
 20. The method asrecited in claim 11, further comprising: detecting an anomaly in atleast the third data sector of the first data track; and when theanomaly is detected in the third data sector, generating second extendedredundancy over at least the third data sector and the fourth datasector of the first data track; and recovering data from the third datasector based on the second extended redundancy.